https://www.bicyclerollingresistance.com/specials/new-vs-worn-gp4000s-ii
Rather than share the results and steal clicks, I’ll encourage everyone to check out the original article above. BRR is a pretty excellent resource IMO. One thing I found very interesting is just how darn durable the GP4000S II is. I’ve always had favorable experiences with that tire personally.
So, no real need to replace tires, especially if they are mounted on race only wheels, every year. I’m curious what the difference is in aero-ness of tires once they are worn a bit.
My guess would be that aero takes quite a hit… to be honest I feel like someone has actually tested that with the GP4000S II but I could be wrong.
https://www.bicyclerollingresistance.com/...w-vs-worn-gp4000s-ii
Rather than share the results and steal clicks, I’ll encourage everyone to check out the original article above. BRR is a pretty excellent resource IMO. One thing I found very interesting is just how darn durable the GP4000S II is. I’ve always had favorable experiences with that tire personally.
Interesting test…but, he seems to make some blanket conclusions about the results that probably don’t follow from this one (particular) test of 2 tires.
For example, he has no idea what the original Crr was of those 2 tires. It’s very possible they were higher than his newer GP4K. It’s not like Conti hasn’t been known to change things over time without announcing, right? :-/
Also, why such a spread between the 2, especially if they were “rotated” as described?
Anyway…my observation over multiple examples is that Crr generally drops with wear, as the tread thickness thins and less material is flexed at the contact patch (and thus, lower losses).
My guess would be that aero takes quite a hit… to be honest I feel like someone has actually tested that with the GP4000S II but I could be wrong.
https://silca.cc/blogs/journal/part-5-tire-pressure-and-aerodynamics
See the “Bonus: Tire Wear and Aerodynamics” section at the bottom
In my mind, I would generally assume less tread = lower crr. The higher crr surprised me.
In my mind, I would generally assume less tread = lower crr. The higher crr surprised me.
Exactly. And that has been my personal observation on tires where I’ve measured the Crr when new and then measured them again after wear. In this case, he didn’t do that.
Another unknown in that test is the effects of the “aging”. Judging by the photos, those tires have been beat. I have 10 year old tires that look better than those…
My fear is that Jarno will take this single result and use it to conclude that tires get worse Crr with wear…sort of like how he takes the tests with latex tubes on MTB tires (and pressures) and then projects those results to road tires :-/
In my mind, I would generally assume less tread = lower crr. The higher crr surprised me.
I would too and that is why, as Tom A also states, we really needed this test to be two tires that he tested originally and then retested two years later. Good idea, but a critical step was missed as we know RR varies from tire to tire within the same make/model and we really needed to age the original tires. I hope he redoes it an ages them properly as I would like to see that data.
In my mind, I would generally assume less tread = lower crr. The higher crr surprised me.
I would too and that is why, as Tom A also states, we really needed this test to be two tires that he tested originally and then retested two years later. Good idea, but a critical step was missed as we know RR varies from tire to tire within the same make/model and we really needed to age the original tires. I hope he redoes it an ages them properly as I would like to see that data.
Exactly. In my tests, Vittoria tires are the gold standard for consistency. I’ve tested 3 of the same model tire back to back and they are all spot on. Contis, on the other hand, are all over the map. I’ve had 2 new tires of the same model that were nearly 5 watts different. I never race on a Conti, unless I’ve roller-tested it first.
I would also add, that I can’t recall a newer Vittoria rolling faster than an older one.
We have wind tunnel data for worn GP4000 compared to new here: https://silca.cc/blogs/journal/part-5-tire-pressure-and-aerodynamics
These were not the same tire at 2 different states of wear but rather 2 tires from the exact mold and batch tested in the tunnel at the same time. Much of the variance you see in Conti tire data both Crr and aero is that there are at least 5 molds for this tire all behaving slightly differently in both categories. Within a single mold, however, the performance is quite repeatable.
Also, all the Crr data I’ve seen pretty much ever has pointed to lower Crr with tire wear, but those were also done using tires controlled for mold/batch, etc and also tires of same age where the wear was done in the test machine… My guess here would be that the lower Crr you would expect from the thinner tread is being offset by the hardening of the tread and/or losses caused by friction interactions in all of the micro cracks of the tread which are really nicely shown in the images.
Josh
My guess here would be that the lower Crr you would expect from the thinner tread is being offset by the hardening of the tread and/or losses caused by friction interactions in all of the micro cracks of the tread which are really nicely shown in the images.
Bingo.
I would venture a guess (just a guess) that the main factor on what reduces a particular tire’s Crr with age/use is the hardening of the tread rubber. New high quality (and fast) tires are typically very “sticky” with great traction too. But, over time as the tire ages, the tread ‘stickiness’ decreases (with a corresponding decrease in traction–but that decrease is usually not a major factor in non-technical TTs) and the Crr decreases too.
Makes me wonder if the old tradition of “aging” tubulars for pro teams and others was an intuitive understanding and appreciation of this phenomenon.